In animal models, though, the results have been more conflicting. While many studies show no effect of artificial sweetener consumption, the latest stud by Kelly Carraro Foletto and colleagues is not the first rodent study to suggest that non-nutritive sweeteners may also interfere in the regulation of compensatory appetite promoting weight gain (Davidson. 2011; Polyák. 2010; Rogers. 1988). This does yet not refute the findings of one of the latest meta-analysis of the effects of low-energy sweetener consumption on energy intake and body weight in man - a meta-analysis published in Nature's prestigious International Journal of Obesity that says...

Figure 1: The forest plots of the practically most relevant data of individual and combined effect sizes for sustained intervention studies comparing the effects on body weight of sweeteners versus sugar (upper panel) and versus water (lower panel) shows that not a single long(er) term study found negative effects - the exact opposite is the case. Even compared to water the use of low-energy sweeteners (artificial or not) lead to measurable, yet not always significant decreases in body weight in human trials (Rogers. 2015).

"that the balance of evidence indicates that use of LES [low or no energy sweeteners] in place of sugar, in children and adults, leads to reduced EI and BW, and possibly also when compared with water" (Rogers. 2015 | my emphasis).

And with respect to the often-cited "evidence" from animal and observational studies, the autors of the meta-analysis submit that...

"[...] the present review of a large and systematically identified body of evidence from human intervention studies, with varying designs, settings and populations (including children and adults, males and females, and lean, overweight and obese groups), provide no support for that view. The question then is whether those hypotheses should be rejected or whether, as seems unlikely, the relevant human intervention studies are consistently flawed in a way that leads, in most cases, to exactly the opposite outcome" (Rogers. 2015)

I do thus want to warn you: Do not overrate the already relatively small amount of extra-weight the rodents in saccharin group of Foletto's recent study gained (see Figure 2, left).

In a previous study, Folleto et al. had already observed that saccharin can induce weight gain when
compared with sucrose in Wistar rats despite similar total caloric intake. In their latest study they did not try to prove that this effect is independent of the rodents' energy intake and mediated by insulin-resistance and / or modified levels of leptin and PYY in the fasting state.

Was it fat they gained or lean tissue mass? Well, I would like to answer these important questions, but Foletto did not disclose (or not even measure?) this important parameter. The practical relevance and reliability of their results is further reduced due to the small cages (44x34x16 cm individual cages) into which the rodents were confined to reduce their voluntary physical activity during the 14 weeks of the experiment, as well as the exclusion of rats who didn't consume the aspired 70% of the planned 75 kcal in form of yogurt per week (the number of rats who fell into this category is also not disclosed).

To this ends, the researchers randomly assigned 16 male Wistar rats to receive ~78kcal per week from either saccharin-sweetened (0.3% saccharin) yogurt or non-
sweetened yogurt (0.5 kcal/g) in addition to chow (2.93 kcal/g) and water ad lib. For 14 weeks, Foletto, et al. measured the total food
intake (from yogurt and chow) daily and the weight gain on a weekly basis (the results are plotted in Figure 2). Fasting
leptin, glucose, insulin, PYY and HOMA-IR levels were measured only at the end of the 14-week study period, though.

Table 1: In view of the fact that any existing negative effects of dietary sweeteners may well be compound-specific. It is certainly worth noting that saccharin is no longer used in modern sweetener formulations of sodas (Wikipedia. 2015)

In spite of the already reported ~5% increase in cumulative weight gain over 14 weeks (p=0.027), the researchers found no differences in HOMA-IR (=insulin resistance), fasting leptin or PYY levels between groups that could mechanistically explain why the rodents who received saccharin sweetened yogurt gained more weight than their peers who received non-sweetened yogurts.

Measurable weight increases are a common pattern in rodent studies particularly for the (today rarely used) artificial sweetener saccharin. It is thus well possible that any existing negative effects are compound-specific. For aspartame, for example, similar evidence is rare to non-existent.

Bottom line: In the absence of a proven theory about the mechanism that may trigger the increased weight gain and in view of the lack of health-relevant data (no information about the body composition of the rodents) and health-relevant side-effects you would usually see in response to pathologic weight gain (changes in insulin resistance, leptin or PYY), I can only refer you back to the quote from the latest meta-analysis of the effects of low- to no-energy-sweetener intake on food intake and weight gain in humans, which say that "the balance of evidence indicates that use of LES [low or no energy sweeteners] in place of sugar, in children and adults, leads to reduced EI and BW, and possibly also when compared with water" (Rogers. 2015).

Whether that's enough to convince you that the unproven negative effects of saccharin on caloric expenditure or increases in the glucose transport mediated by gut sweet-receptors, of which Foletto et al. speculate that they may explain the results of their study, are relevant enough to avoid non-nutritive sweeteners altogether is now up to you. For me it's not enough... | Comment on Facebook!

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